The present invention relates to analysis of polymer resins. In particular, the invention relates to analysis of fluorescent products in aromatic polycarbonate resins.
Aromatic polycarbonates are typically synthesized by reaction of an aromatic diphenol, such as 2,2xe2x80x2-bis(4-hydroxyphenyl)propane (also known as bisphenol A or BPA), with derivatives of carbonic acid, such as phosgene or diphenyl carbonate, in the presence of a catalyst. See, for example, U.S. Pat. No. 3,028,365 to Schnell et al., U.S. Pat. No. 3,334,154 to Kim, U.S. Pat. No. 3,989,672 to Vestergaard, U.S. Pat. No. 4,131,575 to Adelmann et al., and U.S. Pat. No. 5,606,008 to Sakashita et al.; and Japanese Unexamined Patent Publications JP 2000-063507-A, JP 11-005837-A and JP 11-158261-A. When these polymerizations are conducted under melt polymerization conditions, the high temperatures of the reactions and the presence of intentionally added and adventitious catalysts can lead to thermal reactions that convert a portion of the aryl carbonate groups to salicylate esters. As shown below, Fries rearrangement of the linear aromatic polycarbonate I yields, initially, a substituted phenyl salicylate product II, which can then undergo polymerization by reaction of the pendant salicylate hydroxyl group with diphenyl carbonate (DPC) and BPA to yield a branched aromatic polycarbonate III. 
The Fries rearrangement products can also be formed photochemically, and they are observed as side products in interfacial as well as melt polymerizations. The presence of branched polycarbonate III in aromatic polycarbonate resins is generally undesirable because it leads to variations in melt behavior, color and mechanical properties. Also, the primary Fries product II can lead to darkening of the resin over time due to the long wavelength absorption of the salicylate ester moiety and oxidation of the free phenol group. It is therefore important to be able to determine the amount of Fries rearrangement products in aromatic polycarbonate resins and to discover polymerization reaction conditions that minimize the formation of Fries rearrangement products.
Traditionally, measurement of the concentration of Fries rearrangement products (where xe2x80x9cFries rearrangement productsxe2x80x9d refers to all salicylate-containing polymers, i.e., to the sum of the primary Fries products II and branched polycarbonates III) in aromatic polycarbonate resins has been carried out by a laborious hydrolysis of the polymer followed by high performance liquid chromatographic (HPLC) analysis of the resulting small molecules. See, for example, A. Factor, xe2x80x9cMechanisms of Thermal and Photodegradation of Bisphenol A Polycarbonatexe2x80x9d, Chapter 5 in R. L. Clough et al. eds., xe2x80x9cPolymer Durability: Degradation, Stabilization, and Lifetime Predictionxe2x80x9d, 1995, American Chemical Society. Spectroscopic characterizations of Fries rearrangement products of aromatic polycarbonates have been reported in, for example, J. S. Humphrey, Jr., A. R. Shultz and D. B. G. Jaquiss, Macromolecules, vol. 6, pp. 305-314 (1973); C. E. Hoyle, H. Shah and G. L. Nelson, J. Polym. Sci. A., vol. 30, pp. 1525-1533 (1992); I. B. Rufus, H. Shah and C. E. Hoyle, J. App. Polym. Sci., vol. 51, pp. 1549-1558 (1994); and S. Pankasem, J. Kuczynski and J. K. Thomas, Macromolecules, vol. 27, pp. 3773-3781 (1994). Even when analyses were conducted spectroscopically, they involved time consuming sample preparations requiring careful weighing of polycarbonate resin and dissolution and dilution with solvent to form precise volumes of solutions having known polycarbonate concentrations. In addition, the cited spectroscopic methods have no capability to protect from interference by small contaminant molecules that may be present in the polycarbonate resin or in polymerization reaction mixtures.
When modern combinatorial methods are used to screen reaction conditions or catalyst materials, the large number of samples generated can easily overwhelm the traditional analyses described above.
There is therefore a need for an analytical method that enables rapid determination of the concentration of Fries rearrangement products in aromatic polycarbonate resins, that is free from interferences by small molecules, and that is easily automated.
Rapid analysis of Fries product content in aromatic polycarbonate resins is provided by an analysis method comprising:
providing an analytical sample comprising an aromatic polycarbonate;
optionally, separating the analytical sample to yield a high molecular weight fraction;
performing an in-line determination of aromatic polycarbonate concentration in the analytical sample; and
performing an in-line determination of the fluorescence signal due to Fries rearrangement products in the analytical sample;
wherein the total analysis time is not greater than about 5 minutes per sample.